class CPU:
    def start(self):
        print("CPU starts.")


class Memory:
    def load(self):
        print("Memory loads.")


class HardDrive:
    def read(self):
        print("Hard drive reads.")


# 外观
class ComputerFacade:
    def __init__(self):
        self.cpu = CPU()
        self.memory = Memory()
        self.hard_drive = HardDrive()

    def start_computer(self):
        self.cpu.start()
        self.memory.load()
        self.hard_drive.read()


# 客户端代码
computer = ComputerFacade()
computer.start_computer()

'''
CPU starts.
Memory loads.
Hard drive reads.
'''